Thyroid hormone is synthesized in vivo in the form of thyroxine (T4), which is an inactive form, released into the blood, converted to triiodothyronine (T3), which is an active form, in each target tissue, bound to α receptor (TRα) and β receptor (TRβ) of thyroid hormone receptor (TR) classified as a nuclear receptor, functions as a transcription factor in the cell nucleus and provides a physiological action characteristic of each target organ. T3 is metabolized in the target organ and primarily excreted in bile. The physiological action of thyroid hormone in mammals plays a very important role in the growth and differentiation, as well as maintenance of vital function such as control of heart rate, blood cholesterol and triglyceride concentration, systemic metabolic rate and body weight and the like. In terms of pathologic physiology, tachycardia, arrhythmia, cardiac failure, as well as feeling of fatigue, rapid breathing and beating, decreased skeletal muscle, osteoporosis and the like are observed in hyperthyroidism such as Graves' disease (non-patent document 1, non-patent document 2). On the contrary, beneficial phenomenon for the treatment of metabolic diseases such as decreased blood cholesterol, increased basal metabolism and the like are also observed. Conversely, decreased heart rate, increased blood cholesterol and increased body weight are observed in hypothyroid (thyroid hormone deficiency) caused by hypophysis disorder, congenital dysfunction and the like.
Assuming specific exertion of the advantageous aspects of thyroid hormone such as decreased blood cholesterol or increased basal metabolism while avoiding harmful event such as increased heartbeat and the like, and aiming at liver-specific accumulation of the compound, the development of several kinds of thyroid hormone analogues was tried (non-patent document 3, non-patent document 4). As a result, however, an influence primarily on the circulatory system could not be avoided, and the development thereof has not made any progress (non-patent document 5).
It has been reported that thyroid hormone receptors include receptor subtypes of TRα and TRβ (5 kinds of TRα1, TRα2, TRβ1, TRβ2 and TRβ3 including splice variants), and each receptor shows different tissue distribution. That is, it has been clarified that both TRα and TRβ are co-present in the liver wherein 70-80% is occupied by TRβ to be involved in the lipid metabolism and, in the heart, TRα receptor is involved in increased heartbeat and increased cardiac output (non-patent document 6, non-patent document 7).
As TRβ agonist (Thyromimetics), diphenylmethane derivative and diaryl ether derivative (patent documents 1-13), pyridazine derivative (patent document 14), pyridine derivative (patent document 15), and indole derivative (patent document 16) have been reported. However, these have different structures from that of the present invention.